Fused salt cell



S. E. BERGH ET AL May 19, 1959 FUSED SALT CELL 2 Sheets-Sheet 1 Filed July 22, 1957 1 1!. m Lwwiillinvvi FIG. I

INVENTOR. sverre E Eergh FYCKHK El Svni h AGENT Uni S a Paw l" FUSED SALT CELL Sven'e E. Bergh, Lewiston, and Frank E. Smith, Niagara Falls, N.Y., assignors to E. I. du Pont de Nemours and Company, Wilmington, Del., a corporation of Delaware Application July 22,.1957,:Serial No. 673,493

v 3 Claims. to]. 204- 243 1 This-invention relates. to improvements in the construction of a fused salt cell and specifically relates to a method of sealing the cathode leads with flexible bellows type seal and to means to equalize the expansion of the cathode on heating the cell to the operating temperature.

A cell such as the Downs cell for the manufacture of sodium from fused salt is generally constructed with a steel cathode which usually has two opposed leads or arms which extend through the cell wall in order to make contact with the electric power source. When such a cell is heated to the operating temperature much trouble is experienced because of the difierences in expansion of the cathode with respect to the cell wall. Generally on heating the cell the cathode expands to such an extent that the joint is broken and leaks develop in the wall of the cell at the cathode arm entrance. At the same time this differential expansion often results in the cathode becoming displaced unequally with respect to the anode so that the spacing between the electrodes is unequal with resultant inefliciency of production and generally shortened cell life.

It is accordingly an object of the present invention to provide a flexible leak-proof seal at the juncture of the cathode arm and the cell wall. It is a further object to provide positive means to prevent the unequal movement of the two arms of the cathode with respect to the cell structure. Other objects will become apparent from the further discussion of the invention.

Briefly, this invention provides a bellows type seal be tween the cathode arm extending out of the cell and the inner cell wall and also provides a stop at the opposing ends of the cathode arms so that on expansion the cathode will expand in both directions to substantially the same extent and thus maintain the cathode in proper alignment with the anode.

Figure l is a vertical section of a part of a fused salt cell showing the electrode arrangement in detail but omitting the upper and lower parts of the cell.

Figure 2 is a horizontal section of the same cell at AA of Figure 1.

Each designating number refers to the same element in both figures. Steel shell 1 encloses the electrolytic cell which is lined with refractory brick 2. The metal cathode cylinder 3 is disposed around graphite anode 4. Electric power is conducted to cathode 3 by way of opposed cathode arms 5 which extend through the cell wall and are supported thereon by way of sliding blocks 6. The anode 4 enters the cell through the bottom by way of means not shown. The flexible metal seal 7 can be referred to as a bellows seal and is integraHy attached to the cathode arm 5 as by welding at 8. The outer edge of the dished flexible seal 7 is securely attached so as to be leak-proof as by welding at 9 to a metal member 10 which is part of the cell wall but electrically insulated from the steel shell 1. The inner part of flexible seal 7 is attached so as to be leak-proof to the cathode arm 5 as by welding at 8 to the arm. Expansion limit stops 2,887,448 m e s! M 419.

11 are attached by way of electrical insulators 12 to brackets 13 which in turn are attached to operating floor support 14. Expansion limit stops 15, 15 or 16, 16 or both sets may also be used in place of stops 11. Stops 15 and 16 are fastened directly to the cathode arm at predetermined distances from the inner wall member 10 so as to equalize the expansion of the cathode in the opposed directions.

By means of the bellows type flexible metal seal 7 there will be no leakage of bath or distortion or break in the cell wall when the'cathode" 3 heatedfrom room temperature to say about 600 Qin'the-case of the fused 'sodium salt cell" when the cellis placed in operation. 1 As the cathode expands the arms slide over sliding block 15 l 6 harmlessly. Topreventthe possibility that the cathode expansion will all berelievedby movement of one a'rm only and thus bring about uneven centering of the anode 4 with respect to the cathode 3 suitable stops are provided so as to insure that both cathode arms will move substantially equal distances. These expansion stops can be placed outside (outside stops) the cell as indicated by 11. These stops are so spaced that after the cathode has been heated to operating temperature the cathode arms will each have moved an equal distance thereby retaining the uniform spacing of the anode from the cathode. Alternatively, the cathode expansion stops may be situated within the cell itself (inner stops) as at 16 or 15. In this case the stops are firmly attached to or actually an integral part of the cathode arms. As the cathode expands on heating it is forced to expand by pushing both arms to about equal distances through the cell wall so as to result in uniform spacing between the anode and the cathode.

Other means of stopping the one-sided movement of the cathode arm on expansion with rise in temperature may be devised without departing from the sense of this invention. It is important that the cell wall be protected against breakage and electrolyte leakage by a device such as a bellows or dish shaped seal attached to both the cathode arm and to a member of the cell wall while at the same time insuring the maintenance of uniform spacing between anode and cathode by insuring equal expansion of the opposed cathode arms as the cell is brought into operation.

Thus it is evident that the combined use of the flexible sealed bellows with the expansion stops will ensure equal lateral expansion of the cathode such that the cathode remains in uniform central alignment with the anode as the temperature is raised from room temperature to the operating temperature range of a fused salt cell. The bellows will prevent leakage of bath out of the cell and the cell wall, usually made of refractory ceramic and therefore having a much smaller coeflicient of expansion, will not bulge or break since the cathode arm or lead is able to slide in the wall opening in which it fits and will glide on a slide as shown in the drawing at 6. 4 Since there may be more resistance to the movement of the cathode in one direction, than in the other, the expansion stops on or at the arm moving more easily will stop the movement and further expansion will force movement in the other direction. The stops must be placed at predetermined positions to insure thermal expansion to equal distances of both cathode arms.

The bellows seal will have a dished shape and this concave side of the dish or bellows will be directed to the cell wall and conversely the convex side will face inwardly into the cell. The bellows or dish must be sufficiently flexible to take up the movement of the cathode arm or lead without breaking or exerting undue force or pressure against the wall of the cell. But the bellows must have sufficient structural strength so that it will not crack or break away eitl1er f ron1 the wall member at its peripheral edge or from the cathode arm.

This invention applies generally to cells operating at change is encountered the improvement herein outlined may be applied to advantage.

We ,claim: 7 1..In a fused lsalttelectrolyticcell having a cathode iwith-opposedflsidemrms reaching ,throughthe cell wall,

the ,combinationrcomprising aflexible'dished-shaped metal (liquid seal .between'thetcathode. arm atthe interior junction of said .arm at .,the,ce 1l "wall, .sa,id,'fl ex'ible. seal being ,i ntegrally joined th'e-.;z a.1 1'nland withthe wall and having its concave side facing the wall, said flexible seal adapted to prevent leakage of bath on differential expansion of the cathode andof the cell and positive stops so placed as to equalize the expansive movement of the opposed cathode arms as the cell is heated to operating temperature.

2. The cell of claim 1 inwhich said stops are on the outside of said cell.

3. The cell of claim 1 in which said stops are attached to the arm of the cathode at a point within the interior of the shell wall of said cell.

References Cited in the file of this patent UNITED STATES PATENTS 2,599,363 '-Bennett"et' al. June 3, 1952 2,621,155 Williams Dec. 9, 1952 FOREIGN PATENTS 1',047,182 'France.. Dec. 11, 1953 

1. IN A FUSED SALT ELECTROLYTIC CELL HAVING A CATHODE WITH OPPOSED SIDE ARMS REACHING THROUGH THE CELL WALL, THE COMBINATION COMPRISING A FLEXIBLE DISHED-SHAPED METAL LIQUID SEAL BETWEEN THE CATHODE ARM AT THE INTERIOR JUNCTION OF SAID ARM AT THE CELL WALL, SAID FLEXIBLE SEAL BEING INTERGRALLY JOINED WITH THE ARM AND WITH THE WALL AND HAVING ITS CONCAVE SIDE FACING THE WALL, SAID FLEXIBLE SEAL 